<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>

        /*padding和bolder都会影响盒子的大小
          现有一个大盒子和小盒子，怎么让小盒子在大盒子里居中
        */
        .big{
            width:400px;
            height:225px;
            background-color:red;
            padding-left:100px;
            padding-top:75px;
        }
        .small{
            width:300px;
            height:150px;
            background-color:pink;
        }
    </style>
</head>
<body>
  <div class="big">
      <div class="small"></div>
  </div>
</body>
</html>